1. Field of the Invention
The present invention relates in general to wire cutting machines and in particular to an apparatus and method for detecting the length of a wire blank in a wire cutting machine.
2. Description of the Prior Art
The strain gauge is a well known device in the prior art. The application of strain to the gauge causes changes in the electrical resistance of the conducting elements which are proportional to amount of applied strain. For example, U.S. Pat. No. 2,036,458 to Carlson discloses a telemetric device for determining dimensional changes in a structure. The device includes two spaced anchoring members connected by a framework carrying a pair of coils of wire under tension. As the two anchoring members are moved relative to each other, the tension in the coils changes and the resistivity of the wire is proportionally altered.
The strain gauge has many applications in mechanical devices. U.S. Pat. No. 2,442,938 to Ruge discloses a fluid pressure responsive apparatus utilizing electrical strain gauges. Fluid pressure is introduced to the interior of a bellows which is mounted at one end upon a rigid base. The other end of the bellows is freely movable and is engaged with a strain sensitive cantilever beam which is also mounted on the rigid base. As the fluid pressure changes, the bellows causes the cantilever beam to be displaced. Strain gauges mounted on the beam provide an electrical signal which is proportional to the amount of displacement of the beam.
U.S. Pat. No. 4,123,847 to Bosselaar discloses an apparatus for measuring the internal corrosion in pipelines including a pig having a circumferential array of spring-loaded probes for measuring both the average diameter of the pipe and the depth of individual pits. The probes are held against the inside surface of the pipe by spring means. The springs are fitted with strain gauges which receive the tension on the springs. The resistivity of the strain gauges changes proportionally with the tension of the spring and provides an electrical signal representing the amount of movement by the probes.